1. Field of the Invention
The present invention relates to a bottom cultivating machine for forming a soil layer having an uniform field, and a cultivating machine for forming leveled field surface, flat ditches, etc., and more particularly to a field cultivating machine which is suitably applied to a plowing work for turning of soil layer in which a soil pan is leveled and an uniform soil layer is formed on the basis of the leveled soil pan, and which can form not only a flat field surface, but also a flat drainage, a flat ditch, etc. in parallel to and along the reference plane.
2. Description of the Related Art
In order to effectively use a field, it is important to make the soil environment uniform over the overall field. For this purpose, it has been hitherto considered to merely level the surface of the soil, and no attention has been paid to the inside of the soil. It is most important to flatten not only the surface of the soil, but also the soil pad of the field, particularly to make a soil layer flat and uniform.
In Japan, the rotation of crops between a paddy field and a farm land was previously carried out as a typical manner of effectively using the field. The cultivation of wheat as a secondary crop was degenerated because it was unprofitable in terms of the price competition. The rotation of crops was a method of activating the soil, and thus a new method for the management of fields which can take the same role as the rotation of crops has been required.
The rotation of crops has various advantages: (1) the crops can be stably harvested in high yield; (2) the problem of the repeated cultivation in a farm land can be avoided; (3) the paddy crop in the farm land is high; and (4) the harvest of crops such as soybeans, etc. is high.
However, the rotation of crops has disadvantages: (1) drainage is excessive or bad; (2) manganese is excessively contained in a rotated farm land; (3) there is sterility problem in a paddy field which is rotated from a farm land; and (4) the growth of crops is disturbed due to occurrence of blight in a rotated farm land.
As described above, the rotation of crops between the paddy field and the farm land has the advantages and the disadvantages, however, it is the very reasonable mode of using fields in consideration of various characteristics of the paddy field and the farm land.
A described above, the rotation of crops is suitable for Japanese agriculture. For the rotation of crops as described above or the conversion of paddy fields to farm lands to reduce surplus paddy fields, it is important not only to keep the soil of fields fertile, but also to make the field environment uniform. In order to activate the agriculture, not only the soil of the fields is required to be made fertile, but also the fields themselves are required to be formed in a large scale to eliminate or reduce a cultivation load and increase the crop per area. The elimination or reduction of the cultivation load is achieved to some degree by a recent mechanical development, however, it is difficult to increase the crop per area. Particularly, it is unexpectable to grow crops uniformly in a large-scale field. In order to grow crops uniformly in a large-scale field, the soil environment itself must be uniform. If uniform crops can be expected in the overall field, not only the cultivation efficiency can be enhanced by enlarging the scale of the fields, but also the agriculture itself is activated.
In order to keep the environment of the paddy field in good condition, the paddy field is made transparent and kept in a good drainage condition, and an excessive preparation of the paddy field which may promote a breathing trouble of crops can be prevented. However, the excessive preparation of the paddy field must be carried out for the following reason. That is, a water supply work to a paddy field is restricted in time, and the rice-planting season is also restricted due to the growth of seedling. Therefore, in order to flatten the surface of the paddy field and perform the rice-planting work in a short time, it is necessary to minimize the preparation work of the paddy field for the rice-planting. However, the recent preparation of the paddy field is not directed to its original object, but it aims to complete the leveling work of the surface of the paddy field along the water surface in a short time by stirring the soil with water. This work needs a technically cumbersome labor and difficulties. In addition, the preparation of a paddy field is also used to enhance the effect of herbicide. If the surface of the paddy field can be leveled before water is filled in the paddy field, it is sufficient to perform the preparation work of paddy field only once, and the trouble of the preparation of paddy field does not occur. However, In Japanese agricultural situation where a rotary cultivator is mainly used, it is very difficult to horizontally flatten the surface of the field. This is because in the rotary cultivator, the depth from the surface of the field is used as a working reference and thus the unevenness of the surface of the field is left as it is. Further, the difference in hardness of the soil varies the cultivation depth, and thus the cultivation depth is not fixed. Further, the seeds of weeds are also stirred by the stirring of the soil with a rotary, and the stirring work is further needed to enhance the effect of the herbicide. Therefore, the soil of the surface of the field is greatly displaced for a year by the stirring work of the rotary, wind and the drainage environment, and thus the displacement of the soil must be corrected every year.
The leveling of the surface of the soil is carried out by a leveling machine, however, only the surface of the soil is leveled. Accordingly, a correction work for making uniform the field environment in the overall soil layer, in other words, in the depth direction.
For an ideal paddy field, it is required that an area below the surface soil, ordinarily claypan layer (not the surface of the paddy field) is kept horizontal (leveled). However, in the recent Japanese agriculture, much attention has been paid to the leveling of the surface of a paddy field. This leveling work has been generalized because it can be performed relatively easily. In an extreme case, a paddy field having a horizontal surface can be formed even when there is no surface soil. Accordingly, the water management can be easily performed, and thus it has been hitherto believed that the crop is increased by supplying fertilizer and ideal paddy field is formed. However, actually, it is an apparently ideal paddy field, and the crop is not increased. Even in such a situation, the cultivation has been carried out in consideration of the leveling of the surface of the field because it has been misunderstood that the means. Accordingly "horizontal" is limited to the "surface" of the paddy field. Accordingly, the rice crop of sufficient yield cannot be achieved by merely leveling the surface of the paddy field.